Re: [PATCH v4 2/2] PCI: iproc: Add outbound configuration for 32-bit I/O region

[Ray Jui]

Hi Lorenzo,

On 4/3/2019 4:31 AM, Lorenzo Pieralisi wrote:
> On Wed, Apr 03, 2019 at 08:41:44AM +0530, Srinath Mannam wrote:
>> Hi Lorenzo,
>>
>> Please see my reply below,
>>
>> On Tue, Apr 2, 2019 at 7:08 PM Lorenzo Pieralisi
>> <lorenzo.pieralisi@xxxxxxx> wrote:
>>>
>>> On Tue, Apr 02, 2019 at 04:16:13PM +0530, Srinath Mannam wrote:
>>>
>>> [...]
>>>
>>>>> Ok - I start to understand. What does it mean in HW terms that your
>>>>> 32bit AXI address region size is 32MB ? Please explain to me in details.
>>>>>
>>>> In our PCIe controller HW, AXI address from 0x42000000 to 0x44000000
>>>> of 32MB size and .
>>>> AXI address from 0x400000000 to 0x480000000 of 2GB size are provided
>>>> to map ob address.
>>>> First IO region is inside 32bit address and second IO region is
>>>> outside 32bit address.
>>>> This code change is to map first IO region(0x42000000 to 0x44000000).
>>>>
>>>>> IIUC you are using an OARR0 of 128MB in size to map a 32MB address
>>>>> region, that's what I understand this patch does (and the lowest index
>>>>> corresponds to the smallest possible size - it is far from clear by
>>>>> looking at the patch).
>>>> Yes, lowest index corresponds to smallest possible size (128MB).
>>>> In our controller we have multiple windows like OARR0, OARR1, OARR2,
>>>> OARR3 all supports multiple sizes from 128MB to 1024MB.
>>>> These details are given at the top of this driver file, as shown
>>>> below. all windows supports 128MB size still we must use OARR0 window
>>>> to configure first IO region(0x42000000 to 0x44000000).
>>>>
>>>> static const struct iproc_pcie_ob_map paxb_v2_ob_map[] = {
>>>>         {
>>>>                 /* OARR0/OMAP0 */
>>>>                 .window_sizes = { 128, 256 },
>>>>                 .nr_sizes = 2,
>>>>         },
>>>>         {
>>>>                 /* OARR1/OMAP1 */
>>>>                 .window_sizes = { 128, 256 },
>>>>                 .nr_sizes = 2,
>>>>         },
>>>>         {
>>>>                 /* OARR2/OMAP2 */
>>>>                 .window_sizes = { 128, 256, 512, 1024 },
>>>>                 .nr_sizes = 4,
>>>>         },
>>>>         {
>>>>                 /* OARR3/OMAP3 */
>>>>                 .window_sizes = { 128, 256, 512, 1024 },
>>>>                 .nr_sizes = 4,
>>>>         },
>>>> };
>>>
>>> Ok so this patch allows mapping an AXI I/O window that is smaller
>>> than OARR possible sizes, why it was not done from the beginning
>>> I really do not know.
>>>
>> Same Iproc driver we use for multiple SOCs, in previous SOCs does not
>> have 32-bit AXI address region to map ob.
>> In the present SOC, 32-bit AXI address region is available so that
>> this change is added.
>>
>>> Now explain this to me please:
>>>
>>>> This patch add outbound window configuration to map below 32-bit I/O range
>>>> with corresponding PCI memory, which helps to access I/O region in ARM
>>>> 32-bit and one to one mapping of I/O region to PCI memory.
>>>>
>>>> Ex:
>>>> 1. ranges DT property given for current driver is,
>>>>     ranges = <0x83000000 0x0 0x40000000 0x4 0x00000000 0 0x40000000>;
>>>>     I/O region address is 0x400000000
>>>> 2. ranges DT property can be given after this patch,
>>>>     ranges = <0x83000000 0x0 0x42000000 0x0 0x42000000 0 0x2000000>;
>>>>     I/O region address is 0x42000000
>>>
>>> Why 1:1 AXI<->PCI address mapping is not possible in (1), how does the
>>> current code works on 32-bit systems and what's the benefit your change
>>> is bringing.
>> non-prefetchable memory range can only support 32-bit addresses, so
>> that we have taken 32-bit PCI bus address in (1).
>> current code does not work in 32-bit systems. In the present SOC with
>> this new change we can access from 32-bit CPU.
> 
> Thank you. I rewrote the log and pushed patches to pci/iproc, please
> have a look (Ray/Scott please do have a look too) and report back
> if that's fine.>

I reviewed the rephrased commit message by you in pci/iproc branch. It
looks very good to me. Thank you so much for helping with this!

Ray

> Do you agree that the initial commit was lacking _significant_
> information ? Please remember that the commit log plays a fundamental
> part in understanding a change and this one is a very important one
> so I am being pedantic on it.
> 
> Thanks,
> Lorenzo
>